The aim of the proposed research is to develop a ligand to selectively complex 82Rb+ in the presence of excesses of Na+ and K+, for use in positron emission tomography (PET). A particular technological innovation would be to use 82Rb complexes in place of 15O for brain scanning. 82b+ is conveniently obtained from an 82Sr generator, unlike 15O, which is obtained from a cyclotron, limiting use of PET. A review of present knowledge shows that no ligands except calixarenes and calixacrowns show significant selectivity for Rb+ over Na+ and K+. Molecular mechanics (MM) calculations are used to analyze the factors that enhance selectivity for Rb+ over Na+ and K+. Strategies based on MM are outlined for synthesizing unique complexing ligands that will have high Rb+/Na+ selectivity. If successful, the project would provide a thermodynamically and kinetically stable metal ligand complex capable of crossing the blood brain barrier. PROPOSED COMMERCIAL APPLICATIONS A lipophilic 82Rb reagent available from an 82 Sr Rb generator would mean PET could become much more widely used than at present with the limitation of cyclotron produced 15O water. One can estimate the sales of a lipophilic 82 Rb reagent at present levels would yield S30,000.000 annually, with a rapid nose as PET became more widely used.